1. Field of the Invention
The present invention relates to a stress resistant plant and a method for producing the stress resistant plant. More specifically, the present invention relates to the breeding of a stress resistant plant by introducing a cell death suppressing gene into a plant.
2. Description of the Related Art
Today, research on programmed cell death (hereinafter, simply referred to as "PCD") of multicellular organisms has become enthusiastic. PCD is appreciated as essential to ontogenesis, homeostasis, resistance to environmental stresses, or the like of an organism. Research on PCD is mainly performed on Caenorhabditis elegans (hereinafter, simply referred to as "C. elegans"), drosophila and mammals (e.g., Miura et al., Cell Technology, vol. 14, No. 2:145-153, 1995). For example, research on C. elegans revealed some cell death genes (e.g., ced-3 and ced-4) and some cell death suppressing genes (e.g., ced-9). The cell death suppressing genes are considered to negatively regulate activities of the cell death genes, thereby suppressing random cell death.
A protein encoded by a bc1-2 gene found in mammals (i.e., a Bcl-2 protein) exhibits a cell death suppressing activity in cells of various systems (i.e., cells of lymphoid system, nervous system, reproductive system and epithelial system). So far, cell death which may be induced by various processes is known to be suppressed by overexpression of Bcl-2 (e.g., Eguchi et al., Experimental Medicine, vol. 13, No. 16, 18-23, 1995).
Recently, many genes encoding for Bcl-2 related protein and Bcl-2 binding protein are reported. These genes are classified into a Bcl-2 family. Examples of genes belonging to the Bcl-2 family include bcl-2, bax, bcl-xL, bcl-xS, bad, bak, Al and Mcl-1 genes derived from mammals, a ced-9 gene derived from C. elegans, and a BHRF1 gene (derived from Epstein-Barr virus) and a LMW5-HL gene (derived from African Swine Fever virus) (Takayama, Experimental Medicine, vol. 13, No. 16, 24-31, 1995). Generally, it is known in the art that identity and similarity among the genes belonging to the Bcl-2 family are very low at a nucleic acid sequence level and also at an amino acid sequence level. For example, identity between Bax.alpha. and Bcl-2 is about 21% and similarity therebetween is about 43% at their amino acid sequence level (Yamamoto, "Intercellular Signal Transduction", Experimental Medicine, supp., Adduce Co., Ltd.).
Study on PCD of higher plants has just begun recently (see Fukuda et al., Kagaku TO Seibutsu, 34:586-594, 1996). Plants are always exposed to severe stresses. For example, a plant may be infected with virus or bacteria, may be irradiated with UV light, or may be affected by peroxide caused by herbicide. In order to withstand these stresses, for example, in the case of a virus infection, a hypersensitive response (HR) induces PCD. The HR is characterized by the rapid appearance of necrotic lesion at the site of the infection. Although the HR involves some tissue damage, its results is to protect the plant by limiting the spread of the infection. Again, such PCD in a plant is considered to involve the cell death gene and the cell death suppressing gene.
Seeing that a cell death suppressing gene is presumably capable of negatively regulating cell death resulting from stress (i.e., capable of preventing cell death) or the like, the cell death suppressing gene is considered to have resistance against stresses. Accordingly, in breeding a plant, the plant may be conferred resistance to stresses by expressing a cell death suppressing gene. Providing a plant which is conferred resistance to environmental stresses is a vital subject in the field of agriculture. Today, the amount of UV (UV-B) light that we are actually receiving is increased by about 6.8% per decade due to destruction of the ozone layer, and the like. Apparently, plants, are also confronting this environmental problem.
However, at present, to the extent that the inventors are aware of, prior to the filing of Japanese Patent Applications Nos. 9-56743 and 10-8056 on which the present application claims priority, no study has been made to the use of a cell death suppressing gene for acquiring resistance to environmental stresses such as UV light, a herbicide which generates superoxide and salt stress.